Conventionally, in order to couple an optical fiber to a photonic integrated circuit, an array of optical fibers (well known as a “fiber array” by those skilled in the art) comprising a plurality of single-core fibers aligned along an axis is used. This fiber array is conventionally secured on the upper face of the photonic circuit in such a way that each fiber of the device is opposite an optical array coupler formed in the photonic circuit. The device is inclined by a few degrees with respect to the normal to the upper surface of the photonic circuit in order to improve the coupling. Optical array couplers comprise at least one diffracting periodic array formed by an alternation of two thicknesses of semiconductor film, wherein one film is partially etched.
Thus, the light rays coming from the optical fibers arrive onto the photonic device in a preferential direction, which means that the waveguides coupled to the optical couplers extend in that direction.
Optical couplers are therefore conventionally produced on the edges of the circuit, the waveguides extending towards the inside of the circuit.
In order to increase the data rate of data that can be transmitted in an optical fiber, it is possible to use multi-core optical fibers. However, the coupling of such a fiber to a photonic integrated circuit by means of array couplers is difficult because each of the couplers have to be disposed opposite one of the cores of the fiber and therefore very close to each other. Each coupler comprises at its output one or two waveguides formed in a semiconductor film of the photonic circuit and whose routing complies with constraints, notably with regard to radius of curvature. In fact, these waveguides, whether they are strip waveguides or rib waveguides, are formed from two thicknesses of semiconductor film used for forming the array structure of the array couplers, these thicknesses being optimized for the performance of the couplers but which impose constraints regarding the minimum radius of curvature to be complied with.
Unless the photonic circuit comprises several layers of semiconductor film, which is complex and costly to produce, the routing of the light signals is carried out in a single plane and the waveguides generally cannot intersect, which gives rise to strict topological constraints. In the case of an assembly of array couplers intended for coupling the circuit to a multi-core fiber, the disposition of the waveguides at the input/output of the couplers therefore imposes constraints on the arrangement of the optical signal transmitting and receiving circuits.
An arrangement that is as symmetrical as possible is generally sought for the microwave electronic devices coupled to the optoelectronic transmitting and receiving circuits disposed at the ends of the waveguides coupled to the optical fibers, which is not always possible when a multi-core fiber is used.
There is therefore a need to be able to couple the optical fiber to different places in the photonic circuit, irrespective of the preferential direction, notably in order to increase flexibility and compactness in the design of the circuits.